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Would biplanes be of use in VSTOL applications? What is the down side to biplanes? ex. Bush Pilots or VSTOL competitions
I feel like bush pilots and VSTOL competition aircraft could use biplanes to work much better. Granted, range and speed are decreased, but besides overall efficiency, what is the down side to biplanes?

Possible duplicate of Why are there no longer any biplanes?

Possible duplicate of What special handling characteristics or techniques do biplanes have?

Voting to leave open, the bit about bush pilots and STOL had not been mentioned before.

Bush pilots still care about their drag. Gas ain't any cheaper in the bush and the weight of the trip fuel also matters. So they trade a bit of efficiency for good climb performance and short take off, because that's necessary to get out of some places, but not too much of it.

Not that a Tiger Moth is a STOL.. but Whew! https://www.youtube.com/watch?v=kFhKkYmSIp0

The Antonov An-2 biplane has exceptional STOL characteristics.

You're quite right in not doubting the capabilities of biplanes, like Curtiss Pitts with the fully aerobatic Pitts Special.

Aerodynamically, the classic biplane has many disadvantages, with drag being built in everywhere. Like designing an aircraft with a built-in airbrake that is deployed all the time. The double wing creates more drag than a single wing, the struts create extra drag, and the cross-wires between the wings are easy to miss on photo's but are huge contributors to drag as well.
Structurally though, a biplane design is quite advantageous. The biplane configuration acts like a box design, much easier to integrate with the fuselage than the cantilever clean wing with its bending moment at the wing root. So if the construction is exposed to high acceleration like a fully aerobatic plane, there is less aeronautical engineering involved. As usual in aeronautics, aerodynamic disadvantages equate to structural advantages.
But zooming out even further, it makes little sense to create lift together with a lot of drag. Aerodynamics determines the stall speed of an aircraft, the biplane has no advantages here. If the objective of the bush pilot is to fly slowly and inspect, and to have VSTOL capabilities, there is a much better option available: the autogyro. The owner of Quobba Station in Western Australia has built one himself and uses it for inspecting his huge property. They are used as airborne motorcycles for sheep mustering etc. Upon engine failure (which has happened), it can be landed safely anywhere on the property. Just bring a hat.

Update
The thought that biplanes must have slower stall speeds than comparable monoplanes keeps nagging me, but I cannot find an explanation or indication that that is actually the case. For instance for the Tiger Moth: Stall Speed = 40 KIAS @ 827 kg. For the Cessna 172: Stall Speed = 40 KIAS @ 1145 kg.
A biplane could be designed for lower stall speeds and good climb performance: make the wing area much larger than required, with an associated lower wing loading. But this can be done in a monoplane as well:

Simply use a large single wing.
Increase wing area in landing/low speed configuration by using Fowler flaps.
Increase wing camber in landing configuration.

And then it becomes a matter of economics, is it cheaper to build a biplane than it is to build a monoplane with fancy flapping arrangements? Probably. But all the dragginess will cause much higher fuel consumption, and it will take a long time before the pilots get to where they want to be.

Thx for the edit, typing on an ipad is hard.

Biplanes can be built lighter and can have a lower wing loading than monowings. That is the only reason why they might have lower stall speeds. But then they will be painfully slow in flight.

@PeterKämpf have amended the answer.

Re "The double wing creates more drag than a single wing" -- re you speaking specifically of interference issues? Or are you suggesting that 4 wingtips intrinsically create more drag than 2?   RE the latter idea: imagine a monoplane flying along.  Imagine that all of a sudden a second identical monoplane with the identical design (including aspect ratio) suddenly appears keeping station in formation a few wingspans off one of the wingtips of the original airplane.  Has the amount of drag created per unit of supported weight suddenly increased, because there are now 4 wingtips rather than 2?

Re : " re you speaking specifically of interference issues?" -- I should have said, interference issues or/and drag from struts, wires, etc-- my "thought experiment" outlined above is best couched in terms of fully cantilever wings-- spaced far apart to create no significant aerodynamic interference -- a configuration which is theoretically possible, though admittedly rare in practice, even in the case of biplanes, triplanes, etc.

Plus, if aerodynamic interference is such a big deal, and if downwash behind a wing is one of the major contributors to such interference, why hasn't the staggerwing configuration (negative stagger, i.e. upper wing located to the rear of lower wing) proven more beneficial and popular? Sounds like a new ASE question in the making...

A biplane would make a terrible bush plane for the simple reason that the lower wing would get torn off on landing due to poor ground clearance.
Burt Rutan tried to make a STOL/Bush biplane called the Grizzly which had two low wings with giant flaps, and abandoned it for this reason. The canard/wing arrangement avoided the aerodynamic deficiencies of stacked wing biplanes. He said he had a fundamentally poor understanding of the need when he designed it.

It's hard to find what Rutan haven't tried :)

Actually, the Barnstormers used Curtiss JN-4s as their bush planes.
Additionally, there is research on High-Lift Biplanes, as well.  Under certain conditions the induced drag from wing interaction is eliminated and lift increased.  This is especially true where the upper wing is swept and the lower wing is elliptical, like the Pitts Special and Christensen Eagle.
https://arc.aiaa.org/doi/pdf/10.2514/3.59846
https://www.skytamer.com/Antonov_An-2.html


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What were the "flap pump" and "gear pump" on the F-4E Phantom II?
When I choose the F-4 in X-Plane 8 there are "buttons" labeled "flap pump" and "gear pump", whose tooltips say something like:

Manually operating and closing flaps/pumps in a failure

So

How did pilots operate these hand pumps? Video is appreciated.
How much "pumping" was needed to open and close the landing gear?
How much "pumping" was needed to move flaps a single unit?
Did you need to be powerful in order to operate these hand pumps?
How did these pumps work?

Maybe somebody has a manual that can answer, I know it can be quite a few pumps. For example, the manual gear lowering pump in a 177-RG is 40 strokes.

Hmm, I just read the entire RF-4B manual and there are no such buttons/switches in it. The emergency procedures for both flaps and gear involve activating high pressure systems, not pumps. Continuing to research, but this may be an anachronism to the game.

The F-4J manual is the same. No such switches exist. I would also point out that in both manuals, in the event of a flap failure, or gear failure, the emergency systems are designed to deploy the flaps and gear. Re-retracting both systems after emergency deployment is contra-indicated and said to be impossible.

How can this question be too broad? It is about one plane, and two switches.

There is no "Flap Pump" or "Gear pump". There is a hydraulic system on the F4 though. All those systems need hydraulic power. They run on hydraulics.

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Why F4 Phantom II didn't have an cannon?
Question is simple but seriously ? Who would design a FIGHTER bomber without an cannon ? What was the crazy reason they didn't added an cannon to it ? (Also My CPU is Athlon X2 II 250.... If only I had an Phantom CPU instead of an Athlon series...)

The reason why they want to do it it is because it's heavy.(900 pounds for the gun, magazine and feeding, and full ammunation) and takes a lot of space. The reason why thought they could live without it is because missiles were thought to be the solver bullet. Just like some phones doesn't have ear phone jacks any more, some computers does not have keyboards, some cars wont have a steering wheel soon. Innovations always seem crazy for its time but time has and will prove some of them ingenious while others indeed insane.

A cool article about the F-4

Later models did have a cannon. Although the early models didn't have a canon (under the assumption they weren't needed anymore after the invention of AA missiles), it was soon found to be a mistake (learned the hard way in the Vietnam War), an internal cannon (M61) was introduced in the E model (and all subsequent ones)

The earlier versions of the F4 used by the US Navy and USAF could be equipped with gun pods housing 20mm cannon and 7.62mm machine guns. These were used quite extensively in Vietnam although mainly for ground attack work.

20mm gun pods used by the F4 in USAF service included the SUU16/A and SUU23/A pods with the M61 cannon, using an air turbine and gas operation respectively to power the gun, while the US Navy used the Mk4 gun pod housing the twin barreled Mk 11 revolver cannon with a rate of fire adjustable up to 4200 RPM.

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Is it unprecedented for an F-16 to get hit by its own bullet(s)?
According to Dutch state broadcaster NOS, an F-16 was hit by its own bullet(s) in a training exercise:

De F-16 die in januari aanzienlijke schade opliep tijdens een oefening boven Vlieland blijkt geraakt te zijn door zijn eigen munitie.

My translation:

The F-16 that in January suffered considerable damage during a training exercise above Vlieland turns out to have been hit by its own ammunition.

They also added a picture of the damage:

Image attribution: originally by Inspectie Veiligheid Defensie, taken from nos.nl.
Comparing that picture with the following stock photo, it looks to me like the bullet that caused the damage entered from the front. Of course it could also be due to the aircraft flying at a high velocity.

Image attribution: "F-16 Cockpit (J-513)" by Gerard van der Schaaf // CC BY 2.0
Is this unprecedented? Or are there any records of other F-16 jets getting hit by or collide with their own bullets?

There's a question here somewhere about planes shooting themselves down. Unfortunately, I can't find it.

@FreeMan this answer to a broader question might be what you're thinking of. Also, this question, but it's about missiles specifically.

No, I saw both of those. I was pretty certain that there was a question about a fighter being able to shoot itself down. Of course, that was a more general question and you're specifically asking if an F16 has ever done that before.

From what I understand the aircraft fired its cannon while in a steep turn, and some of the shells impacted the fuselage as a result. I've heard of it happening before but can't remember where.

I can find no record of an F-16 shooting itself down prior to the Dutch incident. There is certainly nothing on the wikipedia page for aircraft shootdowns or anywhere else I can find.
However its not the first aircraft to manage the feat. In 1956 a US Navy F-11 Tiger became the first aircraft to shoot itself down, whilst testing its cannons on a test flight. The pilot fired a long burst of cannon fire then entered a shallow dive and hit the afterburner, shortly after the aircraft was hit by its own bullets.


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Are there any reported cases of noise from helicopters causing damage to property?
In the Netherlands, three cases have been reported of Chinook helicopters' rattle noise (low frequency sound) damaging solar panels. The Dutch defense ministry recognises this problem and the lawyer representing some of the victims says these may be the first cases (worldwide). Source (in Dutch)
I'm wondering if there are any more of such cases (possibly involving damage to property different than solar panels or involving different helicopters). I found the following literature study on rattle noise (in Dutch, sources mostly in English). The study states that damage to buildings is possible according to laboratory tests, however, as far as I can see it does not name any real world examples of such damage.
My question is if anyone knows of any such damage (different from this report in the Netherlands) to (civilian) property caused by rattle noise from helicopters.

Do you include damage to livestock - cows, horses, &c - scared by low-flying helicopters?

@jamesqf I hadn't considered it, however, if you feel you can write an interesting answer about it that's fully appreciated. :)

Any vibrations close & strong enough can do damage to something susceptible enough. Do you happen to know the minimum distance required between vehicles and property for flight operations in the Netherlands?

@Mast I do not, but there is a public road just next to the end of the runway at Gilze Rijen airport. Unfortunately, Google Streetview is redacted, however, the aerial view shows it pretty well. It does have warning signs for when planes are taking off or landing so you shouldn't cross at those times, no physical barriers (like many railway crossings would have) though.

I was under the impression that helicopters didn't need a runway, but luckily there's clearly a helicopter parked a little north of it, near the hangar. That is quite close to the road indeed.

@Mast On airbases and indeed most airfields helicopters are considered aircraft for traffic control and do use the runways (or grass fields next to them) for operations. Hover taxi to the runway, then fly out following the runway direction.

The article states that it's not even clear the damage was caused by the helicopters, that there is no other known incidence of such damage being caused by helicopters, and that a scientific study has shown that while in theory there could be damage such has not actually been shown to be caused.
In other words, it looks suspiciously like a group of people who want the helicopters gone from a nearby airbase lawyering up with some spurious and dubious claim for which there is no evidence whatsoever, hoping to win public opinion and probably environmentalists rather than having an actual legal case at all.
This is not unheard of in the Netherlands (and elsewhere).
So in short: the article in BN de Stem answers your question already: there is no known instance of such damage happening, and even in this case it's mere speculation that it's happened at all.

So, perhaps the more interesting question is how would you prove that damage was done by a helicopter, but I suspect that's an impossible question.

@stripybadger apart from flying a helicopter over a known good sample under controlled conditions using well described flight profiles until something happens, yeah. And even then you can't prove no damage could ever happen if only a different flight profile or number of exposures had been used.

And it's probably cheaper to replace a few solar panels than make a thorough test flying over a hundred times in possible unconclusive controlled test, also there's all the point in selling a image of being caring and friendly

@stripybadger "How would you prove that damage was done by a helicopter?" You almost wouldn't. You'd show that the damage was consistent with damage that you've shown was created by helicopters under test conditions, and demonstrate that there were helicopters in the area at roughly the time when the actual damage occurred.

@jean even if these claims were found to be true, I wouldn't expect the military base to move. Instead, they might (after lengthy court battles) compensate victims insofar that they would move away. Or they could settle out of court with individual victims so as to avoid legal precedent.

@JJJ indeed. If they just replaced all damaged solar panels they'd effectively admit they caused the damage, leading to lawsuits demanding the helicopters be banned from flying, which is the real reason for the complaints in the first place, cause the helicopters to go away.

Not necessarily. They could settle out of court without admitting guilt. Even if they admitted guilt or were proved to cause the damage, I highly doubt that would be enough for the base (or their operations) to move. By the proportionality principle I think (though IANAL) that the base and its operations trumps minor inconvenience to the public. Compare it to people's houses being demolished to make way for large infrastructure projects. They can protest, but they will get a (large) settlement at best.

@JJJ doesn't matter whether they admit guilt or not. The Dutch press, environmentalists, and other pressure groups would call it just that, admission of guilt, and relentlessly campaign to get the helicopters grounded. That's how it works in the Netherlands.

Er, delete "almost" from my previous comment. I tried to edit from "almost certainly wouldn't" to "wouldn't" and failed.

My question is if anyone knows of any such damage (different from this
  report in the Netherlands) to (civilian) property caused by rattle
  noise from helicopters.

A personal anecdote: I used to live on the flight path of helicopters flying from Aberdeen airport to North Sea oil rigs.  We would also see occasional Chinooks and Tornadoes from RAF Lossiemouth.  We had a plate rack on the wall much like this one.
Two and three bladed helicopters and the Chinooks would make the plates rattle noisily.  5-bladed helicopters and Tornadoes were much quieter by comparison.
As to actual damage: only after multiple choppers managing to setup the right resonance plates (and teacups in a poorly-built cabinet) would move closer to shelf edges, but I don't remember anything breaking because we noticed it and would move them back or somewhere safer.
I can easily imagine loitering helicopters or an increased number would cause more of a problem.  I wonder what they'd do to old cement and terracotta chimney pots.


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What is this helicopter (and probe) in the film "Act of Valor"?

In the film Act of Valor, two helicopters are used to airdrop troops and their boats onto a river. (Clip here.)

Firstly can you identify the aircraft?
Second, what is the extremely long probe on the front? It looks to be half as long as the actual helicopter!

My initial guess would be some type of Chinook and refueling probe but that's purely guessing. Can anyone verify or correct?

I swear it is an MH-47 special missions helicopter, because of the refueling probe? Can anyone back me up on this?

That is in fact an MH-47 variant of the Chinook. I work on CH-47's and they do not have the refueling probe.

Wikipedia Image - PO2 Tamara Vaughn [Public domain]

Welcome to Aviation.SE! Could you perhaps provide a link to more info or a picture? If I search Google it just brings up the Mi-17. You can edit your answer to improve it and/or add more content. You may also want to take our site [tour] and maybe check the [help] to learn how the site works.

Sorry I’d typed MH-17 into google by mistake. Found it now, thanks!

By U.S. Navy photo by Mass Communication Specialist 3rd Class Robyn Gerstenslager [Public domain], via Wikimedia Commons
Yes, it looks to be a Boeing CH-47 Chinook. Above is a photo from Wikipedia showing an Army Chinook with a Navy SWCC boat attached to the external cargo hook, looking almost exactly like in the movie.
And yes, the probe is the refueling probe. It needs to stick out from under the rotors, to prevent the rotors from accidentally cutting the fuel hose. (Although it doesn't prevent this from happening.)

Actually the MH-47 refuel probe is inside the rotor disk. It does not extend out past the rotor system.

JM is not correct on the probe. The probe comes from the nose to create a safe distance from the refueling boom on the other aircraft. Out of the rotor (or anywhere near it) would be absurd. The bird used in the movie Act of Valor was an MH-47 from the 160th SOAR. I know from personal experience. The boom is modified for night-time refueling under NVG's.


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Is it possible for a civilian to use a VORTAC station?
Suppose you have a Cessna 208 Grand Caravan Amphibian and you want to use VORTAC stations on military bases (or somewhere else). Is it possible? Is it legal?

It's legal.  Tuning a VOR signal is different to area based restrictions. If the wanted the signal restricted, they would encrypt it like some GPS signals.

@RodneyHawkins I don’t think it is possible to encrypt a VOR signal, which is what you are tuning to when tracking a VORTAC. If they wanted to restrict civilian use they would put in a TACAN and leave off the VOR.

Totally legal to tune it up & use it. If it is a VORTAC, it will work just like every other VORTAC out there. If it is a TACAN, you may be able to get DME from it, but you won”t get bearing from it without a TACAN receiver.
Many, perhaps most VOR’s out there are in fact VORTAC’s — the TACAN station is colocated with the VOR. It is possible to have a VOR-DME station, which gives a civillian user everything a VORTAC does, but no bearing info to TACAN-only military aircraft. And you can have a VOR station with no associated DME at all.
But you won’t find any rule prohibiting you from tuning up any of the above - doesn’t exist (at least in the U.S., nor anywhere else I’ve ever heard of). If the military wanted a NAVAID they could use that you couldn’t, they could put up a TACAN using a channel that civillian DME receivers can’t pair with (ex ch 16X “pairs” to 135.9 - not a frequency in the range civil VOR receivers can tune to) and not publish it. But realistically, they’d probably just use a GPS coordinate & call it good.
(Edit: as @UnrecognizedFallingObject mentioned, it is not the “Y” TACAN channels that conventional VOR receivers can’t pair with, but there are some channels you can’t get DME from using normal VOR tuning — see this chart.)
Flying over that navaid on a military base may entail issues with the airspace involved, but that is its own issue, unrelated to using or not using the navaid.

BTW: it seems that most DME receivers can use Y-channels (you'll see plenty of civil DMEs published as "Chan 54(Y)" or whatever, see the I-SAJ DME used with the ILS for KORD RWY 09L for ex.)

@UnrecognizedFallingObject - Good catch! Looks like the X channels pair up to frequencies like 112.30, while the Y channels pair up with .05 higher, so 112.35. Edited post above to reflect that.

Absolutely.  A VORTAC is nothing more than a VOR colocated with a TACAN.  Most VOR-DMEs in the US are VORTACs.  If there happens to be one located on a base you are certainly still able to use it.

Short answer: A VORTAC station combines a VOR-DME and a TACAN. It is the result of a cooperation between civil and military worlds to share the same DME (and the navaid place).

Civil aircraft use includes accessing the VOR part (civil), the DME part (civil and military), but not the TACAN bearing transponder, said otherwise they access the VOR-DME equivalent, or for what civilians are concerned, a VORTAC is a VOR-DME.
They are not equipped for receiving the TACAN bearing equipment, though nothing prevent them to be equipped with the related UHF receiver.

More details: A VORTAC station is composed of three signal generators:

A VOR (VHF) signal used for civil bearing determination.
A DME (UHF) signal used for range determination
An UHF signal used for military bearing determination, in theory 9 times more accurate than a VOR.

DME and UHF bearing station components are interrogated by the aircraft, contrary to the VOR which broadcasts continuously.
When civilians use a VORTAC, they actually use the two first signals (VOR-DME). Military use the two last signals (TACAN) and the VOR as a backup if they are equipped, which is normally the case.
Pure TACAN have only the UHF bearing determination signal and the DME signal.

Source
Their little size, compared to a VOR-DME, allow them to be used on ships. More: Wikipedia article on TACAN, and How does Tactical Air Navigation work?


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Do F-4 Phantom II pilots actually fold the wings?
In flight simulator X-Plane 8.15, the F-4 Phantom 2 can fold the tip of its wings (well, variable sweep). Is that useful? Why would a pilot fold the wing? To reduce lift for short landing?

The wing folding is only meant to save space on a carrier during storage, it is not for in-flight use. Are you asking about sweeping or folding?

Seems to be dedicated to parking on aircraft carriers similarly to aircraft operated on carrier operations. There seems to be one occurrence of a flight with wings folded according to this article, but it likely was just an error of operation. Some people might know more about it.

@RonBeyer , In XP 8.15, There is an switch that when pulled all the way down, it makes tip of the wings flat, and Wingtips gets more and more "upright" as you pull it to the top

That is folding wings, it is only meant for carrier storage operations, it has no use in flight, and it is not for in-flight use.

Who says that the F-4 could not fold its wings in flight?

Well, only by mistake or failure, which is not the intent of the question.

Woah, X-Plane 8.15!? 11.20 was just released!

@SnakeDoc And worst of all, Its the demo version... well, open this link and go to the bottom then click the For X-Plane installations prior to version 8, go here. this link has X Plane V1 etc

@JonathanIrons You can fly the demo version of 11.20 for free you know ;P It just limits you to a few aircraft and an area... but if it's demo version vs. demo version, I'd go for the latest one unless your system has some trouble running it :) http://www.x-plane.com/desktop/try-it/

@SnakeDoc poornes is my biggest enemy (Fucked up computer systems straight outta CODBO(MOHAA,COD1/4 Forever/BF V and 2 forever), and stolen WIFI)

@JonathanIrons It is indeed brutal on most computer systems, mine barely runs it smoothly. Well, I'm glad you're enjoying it, x-plane and aviation in general is quite fun.

I'm surprised that no answer has mentioned this famous incident of a F-8 Crusader accidentally flying with wing folded -- https://www.flightjournal.com/f8-wings-folded/ ,  https://www.reddit.com/r/WeirdWings/comments/f00un4/an_f8_crusader_flying_with_its_wings_folded_1960/

In U.S. Navy and Marine Corps F-4 Phantoms, the wing fold mechanism was controlled and powered by hydraulics, since the pilot had to fold the wings after landing for taxiing around on the deck. The USAF versions of the Phantom, on the other hand, had this hydraulic capability removed, and there was a pin in the top of the wing, (if I recall), just inboard of the wing fold, which, if it was protruding, indicated that the wing fold was unlocked. It was, obviously, a critical pre-flight step to check that this pin was flush, not protruding.
There was at least one incident where the aircrew failed to notice that the pin was protruding, and took off anyway. Needless to say, the wing folded shortly after rotation and liftoff, with catastrophic results.

Is there online documentation of that incident?

@rclocher3 here is the incident where one wing folded. The short story is the plane lost control completely after rotation, but the pilots managed to narrowly escape by punching out when the jet was momentarily upright. There was another incident where a pilot took off with both wings folded. He landed safely.

Cool, thanks for tracking those down!

As several of the comments have mentioned, the F-4 have the option of folding the outermost section of their wings, as shown in the picture below.
The main purpose of this was simply to save precious space on aircraft carriers, it had no use when flying. There have been some incidents where wings have either started to fold during flight or where the pilot forgot to unfold before takeoff, but it was not designed for this. Many other naval aircraft have the option of folding their wings in a similar manner, such as the F/A-18.
The F-14 Tomcat uses a completely different mechanism to adjust the wing sweep while flying, and although it had a special "parking setting" for the sweep, it was used to adjust the wing sweep according to the speed of the aircraft.
The A-7 Corsair II and the F-8 Crusader also had wing folding, but in addition they could also adjust the attitude of the wing while flying, primarily to improve visibility for the pilot when landing as seen below.

The F-8 had variable AoA, the A-7 did not.

On our RF-4C's the pilot could not fold the wings the crew chief had to do it. It was part of the 25 hour check to fold them and inspect and lube them.


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How does the pilot control the Dassault Rafale?
In the Dassault Rafale, how does the pilot maneuver the plane? I would expect to see a joystick centered between the pilot's legs. Instead, the Rafale has what appear to be two joysticks on both sides of the pilot. How does the pilot use these two joysticks to control the Dassault Rafale?

The  Dassault Rafale is one of the new generation of combat aircraft which have a side stick rather than a center stick for controlling the aircraft.
The Rafale follows the HOTAS concept- one where the buttons are placed on the throttle lever and the flight control stick allowing pilots to access vital cockpit functions and fly the aircraft without having to remove their hands from the throttle and flight controls.
There are two sticks in the Rafale cockpit on either side of the pilot. The one on the right of the pilot is the flight control stick and the other one is the throttle.

Image from freerepublic.com © Alex Paringaux/Dassault
The side stick controller on the right is connected to the aircraft computer and interprets the pilots input, which are then executed via various controls. The side-stick controller is force sensing with only a little travel, as can be seen in this video.
Rafale has a single throttle for both its engines- the left stick has more travel (compared to the other one) and controls thrust of both the engines through the computer. You can see both the sticks being operated in this video.
This type of arrangement is quite common in modern combat aircraft- both the F-35 Lightning II and F-22 Raptor use a similar arrangement- only difference is that in Rafale, the throttle and side stick look quite similar.

Why not just call it a joystick?  That's the term that immediately comes to mind when looking at it...


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Why would a B-29 consume more fuel at 17 kft than at 9 kft?
According to Wikipedia, one of the factors which almost caused B-29 44-27297 (Bockscar) to run out of fuel and crash at the end of its 9 August 1945 strike mission was the selection of an excessively high en-route cruise altitude1 (my emphasis):

Bockscar took off from Tinian’s North Field at 03:49.  The mission profile directed the B-29s to fly individually to the rendezvous point, changed because of bad weather from Iwo Jima to Yakushima Island, and at 17,000 feet (5,200 m) cruising altitude instead of the customary 9,000 feet (2,700 m), increasing fuel consumption.

This does not make sense; generally, an aircraft’s fuel burn decreases with increasing altitude (due to the thinner air at high altitudes, which causes a given indicated airspeed to correspond to a much higher true airspeed, causing the aircraft to cover more distance in the same amount of time for the same amount of fuel burned [resulting in a lower per-distance fuel burn, and, as an extra bonus, a quicker flight]), all the way up to the altitude where indicated airspeed starts being limited by either declining engine power (as the engines can’t get as much air in the thinner high-altitude air, reducing their power output) or the aircraft’s mach limits (as a given indicated airspeed corresponds to a greater and greater true airspeed with increasing altitude, whereas, below the tropopause, a given mach number corresponds to a lower and lower true airspeed with increasing altitude, due to the progressive decrease in air temperature with increasing altitude in the troposphere), forcing the aircraft to fly at a slower indicated airspeed (which both makes the flight take longer, increasing the amount of time the engines are burning fuel, and forces the aircraft to fly at a higher, draggier angle of attack).
For most aircraft (even those not designed for high-mach flight), indicated airspeed (and, thus, per-distance fuel burn) generally only starts becoming mach-limited around 25-30 kilofeet (below this, approaching the aircraft’s mach limits would require airspeeds that are, except for specialised high-speed fighter and attack aircraft, greatly in excess of VNE, and would cause the aircraft to disintegrate from uncontrolled flutter), or even higher for aircraft optimised for transonic flight,2 so an aircraft’s per-distance fuel efficiency should continue to improve until at least these altitudes, as long as the engines can still produce enough power.  The B-29’s3 engine, the Wright R-3350, is a turbocharged piston engine, and, thus (as the power output of turbocharged piston engines, like that of turbine engines,4 remains fairly flat up to very high altitudes, unlike that of naturally-aspirated piston engines, which drops off very rapidly with increasing altitude, or that of mechanically-supercharged piston engines, which also drops off considerably at high altitudes, although not nearly as much as naturally-aspirated piston engines), the B-29’s indicated airspeed would not be expected to be limited by available engine power below the altitudes at which it would become mach-limited.
Why, then, was Bockscar’s fuel burn apparently higher at 17 kft than at 9 kft, rather than lower?

1: Other factors were a broken fuel pump, which rendered unuseable all the fuel in one of the aircraft’s fuel tanks; the decision to take off with said fuel tank full of useless fuel, rather than defuelling the unuseable tank first to lighten the aircraft; the pilot’s circling at the rendezvous point for three-quarters of an hour waiting for an aircraft that never arrived, when he had been specifically ordered to wait no longer than fifteen minutes; the primary target’s having been covered by smoke and cloud which would not have been there absent the half-hour delay, resulting in the aircraft having to circle over the primary target, burning fuel, for fifty minutes before diverting to the secondary target; and twenty minutes wasted circling over the emergency landing field attempting (unsuccessfully, due to a broken radio) to gain landing clearance even when said clearance was not needed due to the aircraft’s critical low-fuel emergency.
2: Such as, for instance, all modern jetliners.
3: Bockscar was a B-29-36 (“Silverplate”) aircraft, extensively modified from the stock B-29 configuration to enable it to carry nuclear weapons; however, the vast majority of these changes were internal, having no effect on the aircraft’s aerodynamics.  Of the exceptions, one (the use of reversible-pitch propellers on the Silverplate aircraft) would have no effect on the aircraft’s high-altitude performance except in the case of a propeller reversing in flight (hopefully not a normal, or even a common, occurrence), a second (the removal of almost all of the gun turrets found on a stock B-29) would considerably decrease the aircraft’s drag, making fuel burn less critical in any case, and, while the weight reduction (reducing the amount of lift - and, thus, the amount of induced drag - needed to maintain level flight) and more powerful engines (tending to cause the aircraft’s IAS to become power-limited at a higher altitude) of the Silverplates would tend to shift the minimum-per-distance-fuel-burn altitude upwards compared to that of the stock B-29 configuration, even the unmodified aircraft routinely operated at very high altitudes without difficulty, indicating that excessive fuel burn at high altitudes was probably not a big issue even for non-Silverplate B-29s.
4: And for exactly the same reason - the precompression of the intake air compensates for the lower density of high-altitude air.

"the power output of turbocharged piston engines... remains fairly flat up to very high altitudes" only if the degree of boost can be changed to maintain a constant manifold pressure. I'd guess they just didn't have enough boost to be efficient at that altitude.

What were the wind speed and direction at both altitudes that day?


text:
Do different grades of leaded avgas differ in ways other than their lead content?
Although only one grade of leaded avgas (100LL, standing for 100-octane, Low-Lead)1 is in common use today, there were formerly a number of different leaded avgasses with higher octane ratings and tetraethyllead (TEL) contents (things like 100/130 and 115/145), catering to the large, high-compression piston engines of decades past; these higher-performance blends are now produced only in small-volume special-order batches for applications where even 100LL doesn’t cut it, such as air races.
Are there differences between the various grades of leaded avgas other than their lead content, or could one convert 100LL into (say) 115/145 simply by adding more TEL?

1: 100LL is only “low-lead” when you compare it to the even-leadier avgas blends of days mostly past; it still has a considerably-higher lead content than leaded mogas ever did.

Gasoline (both avgas and mogas) grades are distinguished solely by octane rating and lead content.
In theory, the octane rating is the amount of actual octane (C8H18) it contains, with the remainder being mostly heptane (C7H16), hexane (C6H14), pentane (C5H12), etc. As you note, a higher octane rating is needed for engines with higher compression ratios.
A century ago, the only way to get high-octane gas was via distillation, and since actual octane is a tiny fraction of crude oil, this was very expensive. It was soon discovered, however, that adding TEL made gasoline behave like it had more octane than it actually did; the higher octane rating you needed, the more lead you added. Leaded gasoline was born, including the 80/87, 100/130 and 115/145 grades of avgas.
However, just a few decades later we discovered how to "crack" long-chain hydrocarbons into shorter ones. Cracking diesel produced (mostly) gasoline--and with a much higher fraction of octane than gasoline distilled directly from crude oil. This allowed creating a 100-octane grade of avgas without any lead, but some old engines actually need a little lead for other reasons, so 100LL was born.
In short, you can take any grade of unleaded gasoline and boost it to any higher grade just by adding enough lead. Start with a higher grade of unleaded, though, and you won't have to add as much.

From my understanding the leadless octane rating of unleaded fuel is less stable and octane rating declines in storage, and this was/is another advantage to TEL in avgas.

@JohnK If you store gasoline in a vented container, the lighter alkanes evaporate more easily, so the octane rating actually goes up over time.   However, a cold engine actually needs those lighter alkanes during startup, leading to complaints about "stale" gasoline, and it's worse with unleaded which has fewer light alkanes to start with.  Use a sealed container, and both will be stable for millions of years.

Octane rating doesn't measure actual octane content, it measures susceptibility to detonaton, AKA "knock".  So ethanol, which contains no octane at all, nevertheless has an octane rating of 113.

Nitpick - it's heptane, not septane.

@Sean It was called septane back when I took chemistry!  Fixed now.

@jamesqf Exactly what "octane rating" means depends on where you are and what you care about, and it's not critical to the overall point anyway, so I simplified.  Feel free to edit if you think it has a material affect on accuracy or usefulness.

What "other reasons" do older engines need lead for?  My understanding was that lead was bad for aircraft piston engines (sparkplug fouling, etc.), but was tolerated due to TEL's beneficial effect on the fuel's octane rating.

@Sean Older cylinders rely on a microscopic coating of lead to protect the valve seats and guides from wear; newer ones are made from harder alloys that don't need it.  Cars had the same problem, but they don't live as long as planes do.

Everybody has gone to valve seats made from stellite so the lead isn't necessary as a lubricant any more. The TEL would form a oxide with some exotic name I can't remember, and this would lubricate the interface of the valve with the seat as it closes and has to slide a bit as two conical surfaces self-align.  I run mogas in my Lyc O-290 but try to run a tank of 100LL from time to time for the benefit of the valves.  Otherwise the engine does NOT like 100LL and the lower plugs start to foul after only about 25 hrs, even with obsessive leaning.  The odd side effect of mogas is a lot more soot.

Octane is is used as a reference only.  That is to say 100% iso-octane (branched molecule) has an octane value of 100 by definition.  A mixture of 100% heptane (straight chain) has an octane value of 0 by definition.  As pointed out in other replies, the octane value of individual compounds vary a great deal.  Toluene for example has an octane rating of 114. Plus there is a RON and MON octane rating to complicate things. An octane rating by itself only relates to the propensity of the air fuel combustion mixture to burn smoothly rather than detonate.  Detonation is obviously bad for the components, but wear on the valves and other parts is affected by many other things other than octane number.  It just happened that tetraethyl lead was a cheap additive that improved the octane number by a few points without changes to the hydrocarbon formulation and seemed to provide coating on the valves that improved wear resistance.  But you can only get so much improvement of octane number by adding lead, beyond a certain value any improvements to the octane number result from the hydrocarbon composition of the fuel itself.

This does not appear to address the question; it does not relate to avgas at all.

@MSalters It actually DOES answer one of the questions asked, can you increase the octane # just by adding more TEL? (Only for a few points.) The post provides context for this answer, but it does address the original post & its questions.


text:
Do I need to be acting PIC when doing takeoffs and landings for my 90-day currency?
The 90-day currency requirement means that to act as PIC of an aircraft carrying passengers you must complete the three takeoffs and landings. Does this include an aircraft where you are logging PIC time but not the acting PIC?
Could you technically then log the landings/TO's if you've blown your 90 days if you have a friend as acting PIC? The FAR also states this is required if you're operating an aircraft certified for two or more crew operations. Does this mean even without passengers, if you are a required crew member on a two crew ship, you need the 90 day currency?

Related

The regulation does not address whether or not you have to be PIC to establish currency.  It instead states that you have to do "three takeoffs and three landings as the sole manipulator of the controls" and in the "same category, class, and type (if a type rating is required)":

Except as provided in paragraph (e) of this section, no person may act
  as a pilot in command of an aircraft carrying passengers or of an
  aircraft certificated for more than one pilot flight crewmember unless
  that person has made at least three takeoffs and three landings within
  the preceding 90 days, and -
(i) The person acted as the sole manipulator of the flight controls;
  and
(ii) The required takeoffs and landings were performed in an aircraft
  of the same category, class, and type (if a type rating is required),
  and, if the aircraft to be flown is an airplane with a tailwheel, the
  takeoffs and landings must have been made to a full stop in an
  airplane with a tailwheel.

Just to clarify, being the sole manipulator means you’re getting PIC time right? You’re just not acting PIC. And does the section about two crew mean regardless if you have passengers, you can act as PIC of a two crew ship unless you’re current?

@Flak Yes, but the opposite is not necessarily true.  Have a look at this article from the FAA website...does a pretty good job of explaining the nuances of logging PIC time.


text:
What’s the grey altitude depicted in the profile view on Jeppesen charts?
What’s the altitude depicted in grey in the profile view? Why there are some approaches that this isn’t depicted and some are?

The grey areas are the minimum descent altitude (MDA) for each approach segment. Below those altitudes there are hazards in those segments. When you conduct the approach you should be aware of those altitudes and take action if you get too close to them.

Might be worth to point out it even says MDA

@DeepSpace It only says MDA on the final segment because that is the approach MDA (which possibly depends on aircraft category, go-around performance, etc.) and can be found further below on the chart. The previous segments are not labelled MDA because they have a fixed minimum altitude (1250' and 850' in the example above).


text:
What are the different types of procedures for starting a fuel injected engine?
Can someone explain the various types of procedures to start a fuel injected piston engine? What is a cold start, hot start, etc.?
I'm referring to a GA aircraft.

Is there something other than hot start and cold start? Are you interested in procedures for starting?

Sure, I would like to know a bit more in details about starting procedures in a fuel injected engine .

Fuel injected GA engines are pretty reliable, they don't need priming and aren't prone to flooding like a carbureted engine.  Really, it's not much different than starting a car, just turn the key and it either starts or it doesn't.  FYI, terminology such as "hot start" means something completely different for turbine engines.

The key thing that makes FI engines different is how you prime them.  You are using the pressurized fuel injection system itself to do the priming instead of pumping fuel into the intake ports using a syringe pump primer.  You do this by turning the boost pump on to pressurize the system and setting the mixture to rich, which on a crude-ish mechanical FI system like the continuous flow systems used on airplanes, just starts spraying fuel in the injectors as long as the mixture is in, whether the engine is turning or not.
Two main differences from a carb:

The priming procedure is one of timing using mixture, not counting pump strokes.
You start the engine with the mixture in idle cutoff (because with the system pressurized and the mixture not at idle cutoff, it'll be spraying fuel in continuously and you'll soon have a little pond of fuel under the cowl).  You don't advance the mixture until the engine catches.

As far as hot/cold starting goes, the basics are the same as a carbureted engine, more prime when cold, less prime when warm, no prime when hot.  So for a cold engine that uses 6 strokes of a manual primer, with the FI engine it's pump on and mixture rich for some period like 5 seconds, then back to idle cutoff before you crank it.  On a warm engine that uses 2 strokes, the FI version might be 1-2 seconds.  You're doing the same thing, just with a different process.
Because it requires careful timing with prime and then keeping the mixture at idle cutoff until start, it's easier to screw it up and flood the engine by messing up the timing, or to be late with the mixture after it starts and it goes and dies on you.  So they can be a little bit fussy until you get the hang of it.   If you're bush flying on floats in something like an injected C-185, where you need to be able to know you can start right now once you push off from the dock, getting it right really becomes important and hilarity will often ensue (drifting toward rocks or moored boats in the breeze as you scream and curse) if you don't.
At the other extreme, because the injector distribution system is normally on top of the engine where all the heat collects, when an FI engine is hot on a hot day it can cause vapour lock in the fuel distributor and lines (even with the very low Reid Vapour Pressure of avgas) and they just don't want to start at all until the cowling cools down a bit.  Not realizing this, you may decide that it needs priming, so you start priming when it doesn't need it and things have cooled down enough for fuel to start to flow again, and now it still won't start (the raw fuel smell with be a clue).  They can be frustrating beasts.

It all depends on the manufacturer. Please refer to your planes specific POH.
If you are confused about the terms here is a brief primer:

Normal Start - Anytime you start the engine under normal circumstances
Hot Start - Starting the engine under conditions when the engine is hotter than the average ambient air temperature. This could be caused by starting the engine shortly after shutting it down after a flight. The engine could remain hot for as much as an hour.
Cold Start - Depending on the manufacturer’s interpretation, it could mean the same as a normal start (in other words, not hot). It could mean starting the engine when the ambient air temperature and the engine (which has been sitting) are near or below freezing.
Flooded Start - When too much fuel has been introduced into the cylinders to accommodate stoichiometric ignition.
External Power Start - Starting without the use of an onboard battery operational.
Fuel Vapor Formation Start - May be similar to Hot Start in climates with higher ambient air temperatures. It purges the fuel lines of vapor. Vapor can cause vapor-lock (the inability to create sufficient vacuum in the fuel lines due to the compressibility/expandability  of a gas (vapor) versus a liquid.

Here is part of what my POH for the Cessna 172S says:

STARTING ENGINE
  In cooler weather, the engine compartment temperature drops off rapidly following engine shutdown and the injector nozzle lines remain nearly full of fuel.
  In warmer weather, engine compartment temperatures may increase rapidly following engine shutdown, and fuel in the lines will vaporize and escape into the intake manifold. Hot weather starting procedures depend considerably on how soon the next engine start is attempted. Within the first 20 to 30 minutes after shutdown, the fuel manifold is adequately primed and the empty injector nozzle lines will fill before the engine dies. However, after approximately 30 minutes, the vaporized fuel in the manifold will have nearly dissipated and some slight priming could be required to refill the nozzle lines and keep the engine running after the initial start. Starting a hot engine is facilitated by advancing the mixture control promptly to 1/3 open when the engine starts, and then smoothly to full rich as power develops.
  If the engine does not continue to run, set the FUEL PUMP switch to the ON position temporarily and adjust the throttle and/or mixture as necessary to keep the engine running. In the event of over priming or flooding, set the FUEL PUMP switch to OFF, open the throttle from 1/2 to full open, and continue cranking with the mixture in the IDLE CUTOFF position (pull full out). When the engine fires, smoothly advance the mixture control to full rich and retard the throttle to desired idle speed.
  If the engine is under primed (most likely in cold weather with a cold engine), it will not start at all, and additional priming will be necessary.   After starting, if the oil pressure gage does not begin to show pressure within 30 seconds in warmer temperatures and approximately one minute in very cold weather, stop the engine and find the cause before continued operation. Lack of oil pressure can cause serious engine damage.
NOTE
  Additional details concerning cold weather starting and operation may be found under COLD WEATHER OPERATION paragraphs in this section.

This is what my checklist says for the Cessna 172S

NORMAL
  THROTTLE......................................................................¼" OPEN
  FUEL PUMP ..................................................................................ON
COLD ENGINE
  MIXTURE ........................................................RICH 3-5 SECONDS
  UNTIL STABLE FUEL FLOW, THEN CUTOFF
WARM ENGINE
  MIXTURE .................................RICH 1 SECOND THEN CUTOFF
  FUEL PUMP ................................................................................OFF
  BRAKES....................................................................................HOLD
  PROP AREA............................................................................ CLEAR
  MAGNETOS.............................................(ATP 8 seconds max) START
  MIXTURE .................................. (advance smoothly as engine starts) RICH
WHEN ENGINE STARTS
  THROTTLE....................................................................... 1000 RPM
  OIL PRESSURE ................................(in 15 seconds) CHECK GREEN
  MIXTURE ......................................................LEAN FOR RPM RISE
  THROTTLE....................................................................... 1000 RPM
  AMPS (M BATT & S BATT).................................CHECK (positive charge)
  LOW VOLTS ANNUNCIATOR.........................CHECK (not visible)
  FLAPS..............................................................................................UP


text:
Why does a higher load factor increase stall speed?
I think that’s self explanatory, why does load factor (G) affect stall speed? Why does load factor result reaching the critical angle of attack at higher airspeed?

Short answer: centrifugal force makes the airplane think it's heavier than it really is.

What does 'having' a load factor1 mean? It means, by definition, that you are experiencing a force G times your weight. It doesn't matter how it happens: in a turn or loop or turbulence. But in all cases practically all that force (which usually counteracts the weight) comes from lift.
In normal unaccelerated flight, lift = weight. In a more general case, lift = weight $\times$ G. If G > 1, you need more lift than weight.2
How can you get more lift (from the same wing)? Either you go faster, or you increase angle of attack. So inevitably, for a given speed, you'll have to fly at a higher angle of attack, closer to stall. Or in other words, you'll reach stall at a higher speed than normal.
Note that exactly the same thing happens if you 'just' increase your weight, by other means than transient loading with G - say, by having more cargo or fuel. Again, you'll need more lift - with exactly the same consequences.

1 Load factor is applicable in all three axes, but we are implicitly talking about the normal factor in relation to stall speed. When you are accelerating forward or skidding, you'll also have a load factor, but it'll usually be well below 1.0.
2 On the other hand, if G = 0, you don't need wings at all and you'll go ballistic.

The forces on an aircraft in straight and level unaccelerated flight must equal. The horizontal force of lift and centrifugal force (load) must equal. The vertical force of lift and weight (load) must equal. Thrust and drag must equal. At a steady airspeed, increasing weight (load) must have a corresponding increase in lift. To increase lift without changing configuration, you have to increase the angle of attack of the flight surfaces. The same happens when you bank the plane in a turn. Just the degree of force acting in each direction changes.
Total lift and induced drag are both a factor of airspeed and angle of attack. The higher the airspeed, the more lift you have. The higher the angle of attack, the more lift you have. If you have a constant amount of lift, airspeed and angle of attack become inversely proportionate.
If you are in a coordinated turn, you are dividing your total lift between horizontal and vertical components. The horizontal component works against centrifugal force in a turn. The vertical component is therefore reduced to be less than your weight. To stay at a constant altitude, you have to increase the angle of attack by pulling back on the yoke (and trim). The pitching action will increase the load factor.


text:
What is the definition of climb gradient?
I have a hard time understanding this topic. I understand it’s the percentage of rising over horizontal distance. Is that correct?

Your understanding is correct.

For small climb, climb gradient in decimal is almost equivalent to angle of climb in rad (40% gradient has only 5% error in this conversion)


text:
Where does the final approach begin if the glide slope is intercepted at an altitude above that depicted on the approach chart?

The final approach segment for an approach with vertical guidance or a
  precision approach begins where the glideslope/glidepath intercepts
  the minimum glideslope/glipdepath intercept altitude shown on the
  approach chart. If ATC authorizes a lower intercept altitude, the
  final approach segment begins upon glideslope/glidepath interception
  at that altitude.

(FAA IPH, p. 4-53)
Does this paragraph imply that the FAF(FAP) for a precision approach fix (point) begins at the minimum glideslope intercept altitude when you have intercepted the glideslope at an altitude above that?
I always have thought the FAF for a precision approach begins wherever the glideslope is intercepted regardless of a glideslope interception altitude. Have I been getting it wrong all this time?
This question doesn't answer what I'm asking. I'm not asking where the FAF generally begins on a precision approach; I know where it begins and I've cited it above. My question is whether the FAF begins at the interception point even when the glide slope is intercepted at an altitude above the minimum interception altitude on the chart. The definition above from the IPH clearly says the final approach fix is the interception altitude when it's intercepted at an altitude below the minimum interception altitude but is silent on where the FAF begins if it's intercepted at an altitude above the minimum interception altitude.

The final approach point/fix can't "begin" anywhere, since it is a fixed point. The final approach segment can begin in different places.

@J. Hougaard That's true but the FAA still calls the point at which the final approach segment begins a final approach fix, unlike the ICAO which choose to call it a final approach point to imply that the point is not fixed and changes depending on the point the glide slope interception is made. In the same sense, the FAA also call a final approach point a final approach point on some non-precision charts where a final approach point changes depending on where the intercpetion of final approach course is made after a PT

Pondlife's answer on the other question looks like a pretty clear answer to me.

@TomMcW  It's absolutely a correct answer; it just wasn't a clear answer for the OP, and I think his lack of clarity is understandable. A lot of FAA definitions & opspecs and FOM's and such are written to confirm what one already understands to be the correct answer, but they don't necessarily to a great job explaining the answer to somebody who isn't there yet. Knowing the right answer to this question, you & I can read the words of the PCG & say, yeah, that's it, right there. Not knowing the answer, one can read the same words & still be unsure. Thus, my post below. Hopefully helpful.

The FAS begins when you've intercepted the GS, and are at or beyond (below) the charted GS intercept point (altitude).  So if your charted GS intercept is at BONGO at 3000' and you intercept the GS outside BONGO at 4000', your FAS begins at BONGO.  If ATC has you join the localizer at 2500' and you intercept the GS at 2500' inside of BONGO, then that point, where you intercepted the GS, is where the FAS starts on that approach that day for you.
There can be lots of ways to say that, some of which are less clear than others.  But that's the simple, and hopefully clear, answer.  And, maybe, going back to the FAA definition, you can see how what they put on paper matches this concept as stated here.

I guess I read too much into the paragraph. Thank you for your clarification!


text:
Why are fuel tanks in the wings filled first, and why are they used last?
When fueling airliners, why is fuel filled first in the tanks in the wings and then the center tanks? And why do they use fuel from the center tanks first and then from the tanks in the wings?
From my research I've found the purpose is not to give too much stress to the structure of the wings, but I don't understand exactly how it works. How does having fuel first in the wings and leaving it last in the wings help protect the structure of the wings?

What type of aircraft are you referring to? I'm not sure that fuel can be used from the center tank, until there is space in the wing tanks. I used to fuel 747s and DC8s for UPS, and thats how it was explained to me. I might remember it wrong, but it would be helpful if we know what type of aircraft you're referring to.

Having all the payload of a plane concentrated at the fuselage creates a large bending load on the wings in order to support that weight. Storing fuel in the wings allows some of that weight to be placed at the same place where it's being supported, in the wings. Distributing the weight into the wings reduces the loads where the wings meet the fuselage.

Thank you for your clear explanation but your answer doesn't seem to explain why fuel is filled in the wing tanks first on the ground. Can you clarify it for me?

@lemonincider Fueling in this order to anything less than full capacity will maintain the correct fuel allocation before any of it is burned.

It may be valuable to add that wing bending relief of loading fuel in the wings is only achieved for cantilevered wings and not for strut-braced wings.

@ErikE: Even for a strut-braced aircraft, it would relieve some of the stresses on the struts, prolonging their lifespan.

@Sean ok. I don’t know why I didn’t post my source. I can’t remember it, but I know for a fact I learned the info in my comment elsewhere. That likely makes it more reliable.

A minor point - keeping less of the flammable fuel in the body has a safety benefit.
Using up what's in the body first helps keep it further away from the crew and passengers.
In a crash you'd prefer the fuel to not ignite, but of the two locations, its better burning out by the wings than inside the main fuselage.

Empty tanks are a greater hazard than full tanks, see TWA 800.

Probably the main reason why fuel is put into the main wing tanks first is because on some airliners (if not most) the engines are fed directly from the wing tanks. Some airliners have to pump the fuel from center tanks into the wing tanks before the engines can utilize the fuel. So for example, if the flight requires 10,000 pounds of fuel, and each wing can hold 5,000 pounds, plus the center tank holds an additional 5,000 pounds, then you don't want to start in the belly tank, because you'll end up with 5,000 pounds in the belly, and 2,500 pounds in each wing. Then the flight crew will have to do a fuel transfer in flight of 5,000 pounds from the belly tank into the wings. Imagine if the flight only required 5,000 pounds and you started in the center tank. You would end up with the full fuel load in the center tank. When the flight crew arrives to take the plane they will have to transfer fuel into the wing tanks before take-off.
If you are topping off the aircraft, it won't matter if you fuel the belly or wings first. However, another consideration, which is not part of your question is weight and balance on the ground when the aircraft is empty. Some aircraft like the older DC8 has like 8 or 10 fuel tanks in various locations, some are forward of the CG and some are aft of the CG. However, the fuel tanks in the root of the wings are usually slightly forward of CG which helps to prevent tail tipping.

The simplest explanation is that the wings are designed to be the load bearing structure in the air and on the ground.  So, you want the most weight to be in/on the wings.
In other words, you want to keep the weight stress on the wing structure as opposed to the fuselage because the wings are designed to carry weight.
Wing tanks are loaded first because:

That keeps the most weight on the wings.
They will always be loaded.  Center tanks may not be fueled at all on shorter flights.

Fuel is then consumed from the center tanks first to keep the most weight on the wings through the flight.

The weight from the fuel will counter the upward bending of the wings, as nothing but the wings alone must bear the load of the cabin, and all of its passengers/cargo. Using fuel from the wings last will decrease stress on wings, and the joints between the wing and cabin.


text:
Is there a FAR reference for the IFR required reports listed in the AIM 5-3-3?
Section 5-3-3 of the AIM lists "Additional Reports" that "should" be made on an IFR flight. There are 9 of them in a radar environment and 2 more in non-radar. The only reference to the FARs is to 91.183 which lists just 3 items, of which only the 2 dealing with safety of flight (weather / other) apparently apply at all times. What is a reference for the others?
Like, "time and altitude...reaching a holding fix", "change in average true airspeed..." or "vacating any previously assigned...altitude"? Please don't say "the AIM is not regulatory". Failing to do any of these things could, as I understand it, get one violated on 91.13 if there's an incident. But is there any specific regulation beyond 91.183? Like the one about ETA change of more than 2 minutes, except 3 minutes in the north Atlantic seems very specific in a regulatory-like way.

Pretty sure that the answer is no, but I think it's a stretch to say that not making a call per AIM 5-3-3 would constitute careless or reckless operation. ("If there's an incident" suggests that there would need to be at least a few other contributing factors to make something reportable...) I think 91.13 is intended to cover things that are a bit more blatant than simply forgetting a radio call or being off your ETA. We really don't want the FAA issuing flight violations for neglecting best practices, or we'd all be in trouble!

Short answer: the AIM is giving you more details on how to comply with the regulations, it isn't just repeating what the regulations already say.
For context, the AIM itself says in its opening section (emphasis mine):

This publication, while not regulatory, provides information which
reflects examples of operating techniques and procedures which may be
requirements in other federal publications or regulations. It is made
available solely to assist pilots in executing their responsibilities
required by other publications.

Going back to 91.183(c), it says that a pilot must report:

Any other information relating to the safety of flight.

A pilot might wonder exactly what information the FAA thinks is related to safety of flight, and how many reports ATC really needs to receive. The AIM provides guidance by listing specific reporting items. It's like the FAA is saying "report these things and you'll (probably) be in compliance with 91.183(c)".
Another example is 14 CFR 91.103, which says:

Each pilot in command shall, before beginning a flight, become
familiar with all available information concerning that flight

"All available information" is very broad and the AIM provides more specific guidance in a couple of places including 5-1-3(b), which essentially says "check NOTAMs before your flight". I assume most pilots would agree that checking NOTAMs is an obvious and essential preflight step, but 91.103 doesn't mention them at all.
In other words, these are examples of the AIM giving more details on how to comply with a regulation; it isn't just repeating the regulation.
You might still ask, if these things are so important then why aren't they in the regulations in the first place? One very general answer is that changing regulations is extremely slow and difficult, whereas the FAA can publish a new version of the AIM whenever it likes. Procedures and technology change much more quickly than regulations can, and there's far too much technical detail in aviation for it to be practical to have it all in the regulations themselves.

This is fine as far as it goes, but I guess I’m puzzled by the specifity of things like “climb or descend at 500 ft/min” and the “ETA+/-2min except in the North Atlantic where its’ 3 min.” things. They are very specific but there’s no reference given for their source, which must exist somewhere else.

Why do you say a source must exist elsewhere?  Can’t the AIM be a source?

@FosterBoondoggle The AIM is full of very specific details that presumably come from many different sources: regulations, ACs, technical studies, the TERPS, ICAO standards, international agreements etc. Listing the source for each one would likely make the AIM a lot longer than it already is. Having said that, there's obviously a reason of some kind for everything, even if that reason isn't easy to track down to a single source.


text:
For purposes of the FAA instrument written, which system becomes primary for pitch following an AHRS failure?
Sheppard Air claims to have questions exactly from the FAA test. I'm wondering what folks think of the Q&A for this one. It asks

In the event of an AHRS failure, what becomes your primary pitch instrument?

The given answers are

PFD altimeter
Standby altimeter
Standby attitude indicator

I thought (2) was correct, but they give (1).
What I find puzzling about this choice is that the AHRS is a measurement system that displays its output on the PFD. So if the AHRS has failed, the PFD will too. The section of the FAA handbook in their explanation refers to using the PFD altimeter for partial panel attitude reference, but says nothing about the context being failure of the AHRS. I'm wondering if I misunderstand what's meant by "PFD" and "AHRS", or is this just stupid FAA word games? (Or a Sheppard Air mistake?)

AHRS only gives pitch/roll/heading. If that fails, the PFD will still have attitude and airspeed data from the ADC.

StephenS beat me to it.

The AHRS is the Attitude and Heading Reference System. It is synonymous to the Gyroscopic systems of a steam gauge aircraft.
The ADC or Air Data Computer is synonymous to the pitot-static system in a steam gauge aircraft. Just like a steam gauge aircraft, the AHRS and the ADC are two separate systems. And, for good reason. They compliment each other while at the same time providing a redundant backup when needing to fly partial panel.
The PFD is the Primary Flight Display. It is synonymous to your PC computer monitor. If your PC is not working, it does not mean that your monitor won’t work. And if your PFD does not work, a TAA will have an MFD (Multi-Function Display) that can display the same info.
That being said, the AHRS is not as important in VFR flight as the ADC. Ask yourself the question of which parts of the AHRS are required by subsections b & c of Title 14 Code of Federal Regulations Part 91.205. No gyroscopic instrument is required by 91.205 for VFR flight. As long as the magnetometers are working and displaying properly, you are still capable of flying relatively safely. Even if the magnetometers are inoperative, you should still have your magnetic compass to meet the requirements of sub-section b.

Could be clearer that the PFD displays data from multiple sources at the same time (unlike your PC/monitor example), and if one source fails, data from other sources isn’t affected.

@StephenS - It’s more like the PFD is the computer and the AHRS and the ADC are just peripherals.

That would be a better example, yes. If your keyboard stops working, you can still use the mouse, at least for the things a mouse can do.

Tbere's TAA in second paragraph?? What's that.

@John  TAA stands for Technically Advanced Airplane.  I converted your post to a comment -- please don't use an Answers post to ask questions.  With a little more rep, you'll be able to leave comments, and you can already use the "Ask Question" button to ask a new question.


text:
Why not use the alternate static port at all times?
One of my club's small planes apparently has an intermittent problem with moisture in the static port line, so the recommendation is to always fly with the alternate static port open. That leads me to wonder why (1) the plane in question (a 172) was not simply designed to receive static pressure from inside the cabin, thereby avoiding this kind of problem and (2) if there's any downside (other than slight miscalibration of speeds and altitudes) to doing so.
I'm aware of the venturi-effect related pressure diff between an external static port and the cabin pressure. That just seems like a calibration issue for airspeed and altitude measurement.
tl;dr: Why are/were GA planes designed with external instead of cabin-side static ports, other than to give the examiners a tricky thing to ask us about?

Internal air pressure changes slower than external, so things like the climb rate indicator may be inaccurate or slow responding.

@RonBeyer -- It seems unlikely to be a rate-of-change issue-- considering that the effect seems to be worse with the windows open (as noted in the second sentence of this answer https://aviation.stackexchange.com/questions/91204/why-not-use-the-alternate-static-port-at-all-times/91205#91205 )

The problem with the alternate static source is it will over or under-read depending on the status of windows, vents and heating. Look at this excerpt from a Cessna 172 PoH and you'll see there's very significant differences, especially with the windows open at low speeds.

If you use a static source inside the cabin your airspeed your altimeter will over-read, how much again depends on vents, heating and windows. This means you'll be flying lower than you think, how much depends on these factors.
You cannot calibrate for these variables as they change dynamically. How much do you need to adjust your airspeed for heating halfway on, or a window cracked, and how would your instruments compensate? The primary static port is much more consistent.


text:
Can you guide me about the purpose of fine alignment in inertial navigation systems?
I am new in inertial navigation field. I have some confusion about fine alignment process of INS. I want to ask that what is purpose of fine alignment?
I know by process of alignment we find the initial attitude matrix from body frame to navigation frame (reference frame) which normally take place by two step

Coarse alignment
Fine alignment
a. what is major difference between both steps?
b. how fine alignment refine the output of coarse alignment? Does Fine alignment minimize the errors to get more accurate output? or Does Fine alignment re correct the initial attitude estimate by coarse alignment?
c. why sensor bias like accelerator and gyro bias and lever arm error are  estimated in Fine alignment process.

Welcome to Av.SE

INS alignment is a convergent/asymptotical process with no completion. The more you wait, the higher the precision, see Why does IRS alignment take so much time?

@mins Actually it is not asymptotic. As you integrate for longer periods, errors in the integration process add up and cause drift, that is, random walks rarely end up at the starting point. Same effect as clocks: the longer you wait after setting a clock, the more wrong it gets. The measure is known as Allan Variance, see section 5, for example.

@user71659: Seems convergent.

@mins Look at fig 11 in my linked document. At 1000+ seconds for that model, error starts to trend upwards. It's intuitive when you think about it, the longer you run an IRS, the more it drifts.

Coarse alignment is using accelerometers to work out an approximate level by sensing earths gravity by the "non vertical accleromnmeter. BUt that "vertical" is influenced by accelerometer error, earth rotation and local effects, the masses of Hills tides etc do change the local vector, so having gained an approximate vertical from the accelerometers, the true vertical and true north can then be measured by earth rotation and the longe rtyhe fine alignment the better,
In some systems, which know they are stationary, the coarse alignment can be used to calculate gyrodrift, since there should be no rate on the Pitch and roll axes, and heading only earth rate, (for which you need to know latitude..) (Function is sin of latitude)
BUT GPS makes this so much easier (esp when moving) since both position is known and velocities. Stored heading if still valid (ie Ac not moved) helps, but GPS track on the ground = heading, and two GPS antennae spaced apart along the fuselage can also give heading when not moving.
With GPS since its acts as a low drift position system, you can use the data to reduce errors, correct offsets and drifts, but with long time constants ie effectively is "fine alignment" in flight..,.as long as the AC is not manoeuvring.
For strap down systems,  all the above applies to the resolved axis in "earth units" and not the physical axis of the sensors,

I was a Doppler Radar & INS specialist for the Air Force in the 80s, and learned systems for the F4 (flying brick) and the triple carousel system for the C-5A. These systems used mechanical gyros in combination with accelerometers to establish a "Stable Platform". The carousel idea was state of the art then and rotated 1 revolution per hour to greatly reduce drift.
BATH was used for course alignment, which is an acronym for Best Available True Heading and local gravity to start level. It would then spin up and do fine alignment by sensing Earth rotation to determine True North. Typically this took about 30 minutes. Modern systems us laser gyros which aren't affected by mechanical drift.

This answer does not seem to address the questions. It is tangential or informational at best.


text:
Why do Western fighters' afterburner glow is reddish orange while Eastern Bloc fighters' is blue?
Recalling what little physics I know, this could be explained by two factors:

The blue color is given by the characteristic EM radiation of C-H bond breaking, C- and H- radicals forming and recombining with O- radicals to form CO2 and H2O. This is independent of temperature and is the reason why a new gas oven's flames are blue.

The orange color is definitely the characteristic blackbody radiation wavelength of about 1500K, ~1200 degree Celsius. Now the problem is what the source of this blackbody radiation is. The way I see it it's possibly from three sources:

The hot afterburner inner wall,

The soot produced by partial combustion, or

The incandescent exhaust itself.

If the above recap is correct, this means either

the Western afterburners either run a lot dirtier than Eastern afterburners, which is unlikely because F35 and F22 have orange afterburner flames and they must be running squeaky clean to not have their afterburner inner walls coated with soot (amorphous carbon) thus having a huge IR signature because of the high emissivity of carbon, and we do not see black smoke coming from any jet since F4,

or

Western afterburners are a lot hotter than Eastern afterburners, to the point that the blackbody radiation color, which is dependent on temperature, dominates the radical color, which is independent of temperature. This seems to be the logical conjecture, given that the Russians have always been pretty poor on metallurgy.

Does anyone have authoritative knowledge on this subject? This rumor seems to be circulating on the internet forever.

Updates

OK, the exhaust may seem a little purplish, that is caused by the emissive characteristic of H2O.

Or, maybe the Su-27 and the MiG-29 just had a cold start and the inner walls of their afterburners are still cold?

On closer inspection, the orange color seems to be solely coming from the glowing afterburner's inner wall, as opposed to the exhaust, although the exhaust is glowing also. This seems to confirm my guess that Western afterburners run hotter.

OK, I've spoken to some guys from one of the ex-Soviet design bureaus. One of them said the blue color is the result of cold afterburner and Sukhoi afterburner design, the fuel being dumped at acute angles into the center of the cylinder using a few big injectors.

I'm guessing it has something to do with the fuel.

Three photos are, unfortunately, far from representative. Light conditions can make rather big difference to representation of colors, as can exposition (on night photos, the flames usually look white simply because they are partially overexposed). It would be best to compare photos from consecutive take-offs on the same air-show on the same day (that will also minimise difference in fuel as everybody will fuel from the same tank—the fuel standards are not exactly the same, but similar enough that nobody bothers with special fuel).

I've seen jets take off from aircraft carriers in full burner with both orange and blue visual signature.  likewise fully loaded F-16's and F-15's, day and night. (the most pronounced visual impact is an night, of course).  This question does not fit real life.  I think it's place on SE, if it has any place at all, is in physics se.

While not an important point, the F-14 was pretty smoky, and the B-52 still is (though not afterburning)

I also wonder why some of the Chinese fighters are blue while others are orange, even among the ones that uses supposedly the same engine.

It all depends. I don’t think there’s a distinctive color between the two.   I would submit that the photos of the Flanker may be in a early stage of the afterburners lighting versus the photos of the Raptor or the F-35, which appear to be in full afterburner.   The color of the exhaust gas is a function of the stoichiometric mixture of fuel and air ratio. It full burner the mixture is quite rich, resulting in a orange colored flame.   Lower stages of afterburner are probably  much closer to peak stoichiometric mixture.  Incidentally these blue colored flames are indicative of a much hotter exhaust gas temperature than an orange colored exhaust.   I’m not sure of the reason why one is selected over the other.   I can submit that there are plenty of photos of Russian aircraft in afterburner with orange colored exhaust and other pics of western military airplane with blue colored exhaust as seen below.

The blue colour is not indicative of hotter flame—no flame is hot enough to reach that colour of blackbody radiation. It is explained in the question and that explanation is somewhat clearly correct.

The middle photo is probably blue because of this effect. Unfortunately that reasoning does not seem to apply to the third image in the question.

no the blue color comes from characteristic emission of CH+O2 reaction, not blackbody radiation

If the color were solely due to lighting, one should be able to find photos of planes with both colors, right?

It’s unusual but there are a few shots of Fat Amy with a blue AB flame.  https://i.pinimg.com/originals/9e/9b/20/9e9b200e66250919d3f952469532a16a.jpg

And here’s a Raptor in burners http://www.aiirsource.com/wp/wp-content/uploads/2015/08/magnificent-f-22-raptor-night-ta.jpg

The light problem is quite easy, during the day we don't see much of the blue colour as there are other sources of light brighter. At night as seen it shows as a source of light. Then the question arises, why can't we see the Balck body radiation, simple because the  AB exhaust is brighter.


text:
If maximum speed was a priority for modern military fighter jets and bombers, approximately how fast would they likely be?
Burt Rutan talks rather passionately about the lack of innovation in space flight, but also mentions how fighter jet (maximum) speed performance has stalled:

In fact, from what little I know regarding fifth generation fighters, not only has the maximum speed stagnated, but it is degrading.
Traits such as stealth prohibit variable intake geometry and variable wing geometry, the maximum speed appears to never be used in reality, it is probably costly and creates other problems (we only have to look at the SR-71 here). Furthermore, other engine characteristics are probably more desirable, such as supercruise and good acceleration in the range where this is critical and actually useful.
However, in this question I'm asking what, approximately (mach 4, 5, 6?) would the maximum speed likely be, if maximum speed was allocated a similar budget and priority akin to that during the cold war era?
The reason I feel this question can be answered at all, is that I imagine there are some very real, practical problems with very high performance aircraft that require extraordinary solutions to overcome. An answer that identifies where these approximately are would thus go a long way towards a satisfactory answer.
Basically, the crux of this question is to identify if there have been any significant aerodynamic, engine, or other performance related advancements that would enable a fighter jet to travel significantly faster than e.g. the F-15 or MiG-25, while still retaining the same functionality as namely the same types of aircraft.
Similarly for a bomber, it is well-known that sustained mach 3 flight can be achieved by looking at e.g. the XB-70 or SR-71. Even with designs from the 1950s. What is realistic today?
Just to be clear: I'm not expecting an exact figure here, but if there are any studies that have looked into this, it would be a very interesting read. If there are no studies, perhaps someone would want to take the challenge and offer a somewhat comprehensive answer as a conjecture anyway. Any math/physics would be great.
I assume that in order to even begin to answer this question, it must be defined what a "fighter jet" is, must it have an air breathing engine, or can it also have a rocket engine, akin to the X-15? Since I'm asking the question, I will also take the liberty to arbitrarily define this here: The engine type is irrelevant, there may be more than one engine, of different types, of the same type. Whatever would make sense in the context of a fighter jet, or even a bomber. Furthermore, it must be a manned aircraft. If it can reach suborbital flight and beyond, like the X-15, it is still an aircraft (again, arbitrarily defined).
An answer that separates the air breathing and rocket engines as two different categories is fine.
This definition of making if fighter jet/bomber is mostly based on wanting to exclude unmanned experimental aircraft, even if hypersonic aircraft such as the X-43 probably serve as a good reference, I feel they have little root in reality, having no life support, no weapon systems, and perhaps no practical purpose whatsoever beyond data recording.
It may also seem like a pointless question, but this might be quite useful in terms of bridging the gap between aircraft and spacecraft, or any other application one might think of -- suborbital passenger jets, etc.

Unless you specify a range and payload capacity, and even a mission profile, you will never get anything more practical than a research prototype like x43.

You speak about maximum speed having "degraded" as though that was something to be lamented. Actually, as in all things, improving performance in one area must be balanced by compromises in others, and maximum speed, above Mach 1, is of vary minimal utility compared with other factors such as maneuverability, payload, stealth, range, endurance, etc.... All a max speed advantage gives you is the ability to run away from another aircraft that can't go as fast as you, and that only if you have enough fuel to use it.

@user3528438 I did specify it indirectly by giving specific examples such as the F-15 and MiG-25, while these have different payloads they have similar mission profiles, and exact numbers are not important here. I feel the type of answer applicable here is explained well enough in the question itself.

@Charles Bretana it is probably a good thing in one context that it has degraded, as you point out, and negative in another. Developments in military aviation have a tendency to provide useful technology for other sectors too, in particular one example would be space related technology, as the companies that build aircraft has in the past been contracted to build space craft. The closer these technologies are, the more space flight would benefit from it. However, this is almost certainly not the only such case where this would be beneficial.

We not only don't, we can't know. If speed was a high priority, much research would have been done in these decades, with the results we can't predict; new materials/fuels invented, etc. Even on social level, if it was indeed so important, people would (or might not!) put up with sonic booms, noise etc., more or less happily in different countries, with different workarounds in place...

@Zeus Far enough; obviously you are correct, that we cannot know what additional research might provide. However, it should still be possible to provide a conjecture on a "lower bound" of what could be done today. If additional research was poured into it during these decades, it would almost certainly be better, but at least such a lower bound based on what we have today would still provide some guidance. Furthermore, such a conjecture would likely point out at least some of the issues further research is not likely to easily overcome, such as hard physical limitations with no solution.

If we take the pinnacle of fast conventional aircraft development - the SR71 and XB70, we find that Mach 3 is about the practical limit for sustained flight, given current metallurgy. Above that, temperature becomes the limiting factor, as in friction temperature, with the aircraft skin heating up to 600-800 degrees F at a sustained Mach 3. We have yet to develop a material that can sustain higher temperatures while maintaining both the light weight and strength of titanium (SR71) and honeycomb stainless steel (XB70). A failure of the cockpit air conditioning system also means either slowing down considerably, or a well cooked aircrew, very quickly.
The air launched X15 sustained speeds in excess of Mach 6, but only for very short time periods, a few minutes... fuel was the limiting factor there. The X15 couldn't sustain Mach 6 long enough for temperature to exceed it's design, while the SR71 and XB70 could sustain Mach 3 for over an hour. Had the X15 been able to sustain Mach 6, it would have encountered very serious heat problems, instead of the somewhat serious heat problems it experienced in its short dashes to high speed.
So, with current tech, Mach 3 is about the practical limit for sustained flight. Beyond that, the problems increase exponentially. And that's not even getting into the expense... remember that the SR71 required a special, high flash point JP7, plus special oil, plus a lot more. It was retired largely due to the expense of operation.

What stops a rocket powered aircraft/spacecraft from simply approaching suborbital (or higher) altitudes to avoid the problem with heat?

As you decrease the air density, then the type of engine needed to power the aircraft becomes different. A jet turbine engine depends on being able to ingest air (and therefore not requiring an oxidizer tank) to function. This same air that a jet engine uses to generate thrust is what causes the problems with heat. For the air to combust properly in a standard turbine, it needs to be slowed down sub-mach 1 speeds. As you get up at about Mach 2.5+, ram air engines start becoming more efficient.

Increasing the speed of an aircraft results in having to make trade-offs. Drag will increase as the square of the velocity, meaning a doubling of speed will take 4x the power to achieve. This problem is compounded by the fact that it is very difficult to design an engine (and an airframe) that performs really well at super sonic speeds, while still performing well at subsonic speeds.
All design decisions always end up in trade-offs. Increasing maneuverability generally requires doing things that will increase the drag, which means you will require more power to compensate (which then requires a larger engine, which will reduce your maneuverability due to the increased weight).
All of these decisions mean that, in the end, increasing the speed of a fighter inevitably requires the reduction of something else, either turning speed, or weapon payload, or range. While better technology has given us more powerful engines, and new materials and alloys allow us to create more maneuverable aircraft, we've actually seen the top speeds of aircraft go down compared to past fighter aircraft, even though we could create an aircraft as fast as anything from the past, with increased maneuverability and weapon payload in comparison.
These decisions are being made because by reducing the top speed of aircraft, they in return also get better maneuverability, so it's conscious decision to take the higher weapons payload, increased range, and higher maneuverability in place of a higher top speed because a very fast top speed is just not all that useful in warfare compared to everything else. Reconnaissance (which is what the SR-71 was designed for) is better handled by satellites, which can't be shot down in practice, and don't require flying over another country's airspace in a way that is likely to draw their ire. Bombers would rather carry a larger payload, and be fast enough to get to the target, but getting their significantly faster at the cost of a reduced payload won't buy you much. Same goes for fighters, they need to fly around somewhat quickly, but a pure speed advantage over an opponent isn't all that useful either (compared to just having a better fighter). So it's a combination of both physics and specifically what things the military values that just means that there's little value to purely increasing speed.

Thanks for the answer, but this mostly states the reasons why increased maximum speed is not a priority, I've already stated various reasons for this in the question itself, and it is not what the question is regarding. The fact that drag increases as a square of the velocity is true, however, the air density is also a factor there, and the aircraft can simply increase its service ceiling to mitigate this issue -- this is after all how spacecraft manage to reach orbital velocity, something which would not be possible at ground level.

Increasing the service sealing only works when you carry your own oxidizer, at some point there isn't enough air to sustain lift and/or thrust in the engine. So you have to make trade offs, because we don't have aircraft that have optimum performance at all altitudes and speeds. You can make a plane that goes very fast, at the cost of something else. In the end, you're constrained by the military mission you specified above, which has to happen. A fighter jet isn't a fighter jet if it can't fight.


text:
What are the air source settings for on the F-16?
As part of the start up sequence for the F-16, the "air source knob is set to NORM", according to this source:
https://theaviationgeekclub.com/heres-why-starting-the-engine-on-an-f-16-viper-is-different-from-most-other-jet-aircraft/
What is "NORM"? And what is "DUMP" and "RAM" and "OFF"? When are these different settings used? What does this actually control?
I can't imagine that the actual air intake for the engine can actually be closed with "OFF"? The other options also makes no sense to me. Is there any variable geometry on the air intake on the F-16?
Will the engine only start in "NORM" or is it just easier to start in "NORM"?

It appears to me that you are looking at the wrong image. You are looking at the fuel panel. The "air source" knob is on the air conditioning panel (the next image), and it appears to be for pressurization control.

@AdityaSharma Thanks for that! I was indeed looking at the wrong picture. Corrected it now in my question. I still don't understand though, is this really for air conditioning? Is that an essential part of starting the F-16?

That’s the engine bleed air control system in the aircraft. It controls bleed air from the engine for cabin pressurization, anti-G, canopy seal, fuel tank pressurization, and air conditioning as well as the cabin pressurization dump valve.
OFF - engine bleed air valve is closed.  Deactivates all the systems listed above.
NORM - engine bleed air valve is open and providing pressurized air for cabin pressure and air conditioning.
DUMP - cabin air dump valve is open.  Bleed air functions to ventilate cabin and can provide a slight pressure boost above 8000 feet MSL.
RAM - engine bleed air valve is closed and cabin dump valve open.  Cabin is ventilated by ram air through an exterior scoop.
This is not closing or shutting off air supply to the engine, but rather the cockpit and other systems that rely on bleed air from the engine to operate. Bleeder valves are often left open during start up, as this presents less resistance from the compressors, when the JFS crank the engine, and allows the engine to build up core speed much more quickly during startup.  Apparently, the F-16 is started up with those systems in operation.

If F-16 sims DCS and BMS are to be believed, this setting also enables air intake used to cool the avionics, and if you fly with it off you risk breaking the avionics due to overheating.

The real issue here would be the fire control radar (FCR), which is cooled by the bleed air environmental control supply.  If, for any reason, the bleed air system had to be shut off, it would be advisable to turn the FCR off as well. It is possible you could use the FCR for short periods of time w/o bleed air operational, but a flight crew should monitor the warning light display for a EQUIP HOT caution and shut off the FCR immediately, should it become illuminated.